A superconductive cable and a cryogenic cable cooled by a cryogenic refrigerant such as liquid nitrogen are operated at −100° C. to −200° C. In order to transmit power using these cables, it is necessary to connect a room temperature equipment such as a transformer and a open/close switch which are in a room temperature part to a cable in a cryogenic environment, and a cable terminal needs a termination connector.
This termination connector has a great temperature tilt (temperature gradient) from a temperature of liquid nitrogen, which is a very low temperature, to room temperature because one end of the connector is cooled by liquid nitrogen and the like and the other end is led out into the air. A general cryogenic cable termination connector will be explained using FIG. 3.
FIG. 3 is a longitudinal sectional view showing an example of a conventional general cryogenic cable termination connector. A conductor 10 such as a cryogenic cable is connected to a lead-out conductor 3 through a connector 20 as shown in FIG. 3. The lead-out conductor 3 passes through a cryogenic section 11 consisting of a liquid refrigerant layer 5 such as liquid nitrogen, and a temperature tilting section 12 consisting of a refrigerant gas layer 4 which consists of nitrogen gas and the like connected above the liquid refrigerant layer 5. The lead-out conductor 3 passes further through a high voltage lead-out section 13 located above this temperature tilting section 12 and is led into a high voltage terminal 24 located at an air part.
The high voltage lead-out section 13 is separated from the refrigerant gas layer 4 of the temperature tilting section 12 by a flange 6, and mainly consists of an insulator 1 and an oil layer 2 such as insulating oil which is filled inside the insulator 1. A reference numeral 21 indicates an outer pressure vessel and a reference numeral 22 indicates an inner pressure vessel in FIG. 3.
Stress cones of various shapes are usually used as a coating material (FIG. 4) of the lead-out conductor 3 which is thus located in the cryogenic cable termination connector. A stress cone includes an insulating coating 3a which is provided circumferentially around the lead-out conductor 3 such as copper and covers throughout a portion positioned at an upper part of the cryogenic section 11, a portion positioned within the temperature tilting section 12 and a portion positioned at a lower part of the high voltage lead-out section 13. In addition, bell mouth structures 3g and 3g for electric field control are provided near the both ends of the insulating coating 3a, and a flange portion 3k which abuts the flange 6 is provided at the center of the insulating coating 3a. (Patent Document 1)
Furthermore, there is also an example of a lead-out conductor 3 which is provided with a capacitor cone as shown in FIG. 5. In a configuration shown in FIG. 5, a cable insulator 3h is provided around the conductor 3 and a capacitor-cone 30 consisting of a reinforcing insulator 3i and metal foils 3j embedded therein is provided around the cable insulator 3h. (Patent Document 2)